Automatic typewriters of the type that employ a magnetic recording media, such as a magnetic media mounted on a data processing card, have become popular and useful tools in the office. In some such systems a card is driven back and forth under a head which both picks up information from it and records on it, and also erases information from it. The head may be driven across the card to operate on different "channels" thereon. One such head, for example, that used in the Magna I brand of an automatic typewriter has one inductance coil and gap for picking up and recording of information and a second inductance coil and gap adjacent thereto for erasing information. Both of these inductances have circuitry associated with them; the first one having circuitry for translating electrical signals to and from the inductance and the second one having circuitry for transferring an erasing signal to it.
In this environment, a problem of unwanted "noise" was found to exist in the reading mode. The source of this noise was at first unknown, and it was thought necessary in dealing with it to employ a special and expensive head. The present inventor, however, has discovered that the source of this noise is magnetic flux linkage between the erase gap and the reading coil. That is, the erase gap when not being used for erasing, serves as a second pick up and having its core closely associated with the core of the reading gap generates an electric signal in the reading inductance coil. Because the gaps are physically separated and usually physically different, the signal developed at the erase inductance is different than that of the read signal and it is this signal that is the unwanted noise.